Guy's conjecture, which has not yet been proven or disproven, states that the Crossing Number for a Complete Graph of order is
See also Crossing Number (Graph)
Sloane, N. J. A. Sequence
in ``An On-Line Version of the Encyclopedia of Integer Sequences.''
http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S.
The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.